Rigid magnetic disks must possess a final smooth planar surface to avoid interference between the transducer carrying slider and the media surface during operation. As the fly heights of sliders is reduced below 10 microinches in progressively higher density disk drive environments, the reduction or elimination of asperities at the disk surface becomes more critical. Disk substrates are carefully processed and inspected to assure that the surfaces are flat within a few millionths of an inch. A thin film disk, which normally includes a magnetic coating that is less than four millionths of an inch thick, is the most critical environment. The rigid disk substrate, which is most commonly aluminum, but may be of other materials such as glass or silicon, is finished to a smooth planar surface. Following the application of the underlayers, magnetic coating and protective coating, including lubricant, the disk in the final form is burnished or lapped to assure that any remaining or grown asperities are removed prior to glide testing which examines whether the flatness achieves the required functional surface specification.
Prior art devices for providing the burnishing or lapping function on flexible magnetic disks are shown in U.S. Pat. Nos. 4,535,567 and 4,656,790. In U.S. Pat. No. 4,535,567, a pair of abrasive tapes are used to burnish respective opposite sides of a disk with the disk urged by an air knife against each of the abrasive tapes as it passes over a roller. In U.S. Pat. No. 4,656,790, opposed air knives confront opposite sides of the disk with the abrasive tape interposed between the disk and one air knife. In both patents the disk is rotated and the tape is advanced during the burnishing operation.